Systems In High Magnetic Fields Research Articles

Raman scattering of graphene‐based systems in high magnetic fields

We review the different results obtained in the last decade in the field of Raman scattering of graphene‐based systems, with an applied magnetic field. Electronic properties of graphene‐based systems with an applied magnetic field are first described. The phonon response in magnetic field, the magneto‐phono resonance, is then introduced and described for graphene monolayer and multilayer, as well as for bulk graphite. Electronic Raman scattering are then discussed in the context of Landau level spectroscopy, of electron–phonon interaction and of electron–electron interaction. Copyright © 2017 John Wiley & Sons, Ltd.

STUDY OF ACOUSTIC ATTENUATION IN HEAVY FERMION SYSTEMS

Quantum kinetic model together with the introduction of a field-tuned orientation parameter are adopted to study the acoustic attenuations of heavy fermion systems in high magnetic fields. The calculated attenuation-peak results near the critical (magnetic) field (Bc) obtained here resemble qualitatively those measured before in heavy fermion systems.

Negative differential conductivity of two-dimensional electron-gas systems in high magnetic fields

Nonlinear effects of two-dimensional electron-gas systems at high magnetic fields are studied, and a current-driven instability is found to take place in magnetic fields corresponding to integer filling factors of Landau levels. The current instability is ascribed to the occurrence of a negative differential conductivity, predicted theoretically more than three decades ago. Physical origin of the negative differential conductivity is discussed and suggested to originate from an electric-field-induced reduction in the average scattering probability of electrons.

Flux line motion in superconducting(YBa2Cu3O7−d)1−x/(SiO2)x composite systems in high magnetic fields

Superconducting (YBa2Cu3O7−d)1−x/(SiO2)x (i.e.Y123/S) composites with x = 0, 0.05, 0.1, 0.15 and 0.2 were prepared by solid state synthesis. Detailed investigations ofstructural and electrical transport and magnetization in applied magnetic fields(B = 0–9 T) were carried out. The typical double-step superconducting transitions observed both resistively(B = 0) andmagnetically (B = 1 mT) reveal the granular nature of all the samples. The XRD,SEM and superconducting transitions show that addition ofSiO2 mainly influences the inter-grain regions of the samples, leaving the pure Y123 phase inintra-grain regions practically intact. This leads to an interesting behaviour ofM(T,B) andresistivity ρ(T,B) in the samples. The field-cooled (FC) magnetizationM(T) measuredat B = 1 mT shows a dip in the diamagnetic transition at a characteristic temperaturethat coincides with the onset of the second step in the zero-field-cooled (ZFC)M(T) measured in the same field. In the presence ofB≥1 T, the broadening of the superconducting transition revealed byρ(T) below the first step is found to be field-dependent, whereas below the secondstep at lower temperatures the broadening becomes field-independent. The width(ΔM) of the high fieldhysteresis loops (M–B) measured isothermally in the superconducting state initially varies as a power law ofB. Dependingon SiO2 content and temperature, the power law further deviates into either a shallow peak or amonotonically decreasing curve. We show that these results and a host of otherconsiderations point towards an interaction of vortices in inter- and intra-grain regions.

Edge singularities in high-energy spectra of gapped one-dimensional magnets in strong magnetic fields

We use the dynamical density matrix renormalization group technique to show that the high-energy part of the spectrum of an S=1 Heisenberg chain, placed in a strong external magnetic field H exceeding the Haldane gap Delta, contains edge singularities, similar to those known to exist in the low-energy spectral response. It is demonstrated that in the frequency range omega greater than or similar to Delta the longitudinal (with respect to the applied field) dynamical structure factor is dominated by the power-law singularity S-parallel to(q=pi,omega)proportional to(omega-omega(0))(-alpha'). We study the behavior of the high-energy edge exponent alpha(') and the edge omega(0) as functions of the magnetic field. The existence of edge singularities at high energies is directly related to the Tomonaga-Luttinger liquid character of the ground state at H>Delta and is expected to be a general feature of one-dimensional gapped spin systems in high magnetic fields.

Exploring antiferromagnetic S = 1/2 dimer systems in high magnetic fields

We report on measurements of magnetic and thermodynamic properties on two different Cu2+-containing S = 1/2 dimer systems. One is the recently synthesized metal-organic system C36H48Cu2F6N8O12S2 (TK91). At temperatures T < 0.2K and fields around 6T, strong enough to close the spin gap to the excited triplet state, indications for a field-induced phase transition are observed making this system a potential candidate to study the Bose-Einstein condensation of magnons. The second system is the natural mineral Cu3(CO3)2(OH)2(azurite) which was identified as a distorted diamond chain–a realization of a 1D quantum frustrated system. We find a huge acoustic anomaly around 31T accompanying a magnetic soft mode.

Two-dimensional frustrated spin systems in high magnetic fields

We discuss our numerical results on the properties of the S = 1/2 frustrated J1-J2Heisenberg model on a square lattice as a function of temperature and frustration angle ϕ = tan−1(J2/J1) in an applied magnetic field. We cover the full phase diagram of the model in the range π ⩽ ϕ ⩽ π. The discussion includes the parameter dependence of the saturation field itself, and addresses the instabilities associated with it. We also discuss the magnetocaloric effect of the model and show how it can be used to uniquely determine the effective interaction constants of the compounds which were investigated experimentally.

Pinning mode resonances of new phases of 2D electron systems in high magnetic fields

A striking rf or microwave resonance is a generic feature of electron solid phases of two-dimensional electron systems. These resonances have served to identify and characterize such solids, in the insulator that terminates the series of fractional quantum Hall effects at high magnetic field, in the range of the integer quantum Hall effect, and in bubble phases in the first excited and higher Landau levels.

Localized-magnon states in strongly frustrated quantum spin lattices

Recent developments concerning localized-magnon eigenstates in strongly frustrated spin lattices and their effect on the low-temperature physics of these systems in high magnetic fields are reviewed. After illustrating the construction and the properties of localized-magnon states we describe the plateau and the jump in the magnetization process caused by these states. Considering appropriate lattice deformations fitting to the localized magnons we discuss a spin-Peierls instability in high magnetic fields related to these states. Last but not least we consider the degeneracy of the localized-magnon eigenstates and the related thermodynamics in high magnetic fields. In particular, we discuss the low-temperature maximum in the isothermal entropy versus field curve and the resulting enhanced magnetocaloric effect, which allows efficient magnetic cooling from quite large temperatures down to very low ones.

Ground State of Two-Dimensional Finite Electron Systems in the Quantum Hall Regime

We study electronic structures of quasi-two-dimensional finite electron systems in high magnetic fields. The solutions in the fractional quantum Hall regime are interpreted as quantum liquids of electrons and off-electron vortices. The ground states are classified according to the number of vortices inside the electron droplet. The theory predicts observable effects due to vortex formation in the chemical potentials and magnetization of electron droplets. We compare the transitions in the theory to those found in electron transport experiments on a quantum dot device and find significant correspondence.

Magnetoelastic and magnetothermal properties of low-dimensional quantum spin systems in high magnetic fields—a case study

We report measurements of magnetic, magnetothermal and magnetoelastic properties of a new Cu(II)-coordination polymer Cu(II)-2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene (CuCCP). According to our results which cover wide ranges of temperatures 0.06K⩽T⩽320K and magnetic fields B⩽50T, this material presents an almost ideal realization of an one-dimensional uniform S=12 Heisenberg antiferromagnet. Owing to the moderate exchange-coupling constant of |J|/kB=21.5K, it was possible to study the system in its interesting high-field range, i.e., across the saturation field gμBBs=2|J|, which, at T=0, marks the endpoint of a quantum critical line. Using pulse-field techniques the high-field magnetization and elastic constant have been measured. A comparison with calculated magnetization curves reveals a distinct magnetocaloric effect at high fields for T<7.5K, which grows upon cooling. In addition, at temperatures T<|J|/kB, a pronounced acoustic anomaly has been found close to Bs and identified as a generic property of the uniform antiferromagnetic Heisenberg chain with a finite spin–lattice interaction.

Aspects of noncommutative descriptions of planar systems in high magnetic fields

We study some aspects of recent proposals to use the noncommutative Chern–Simons theory as an effective description of some planar condensed matter models in strong magnetic fields, such as the quantum Hall effect. We present an alternative justification for such a description, which may be extended to other planar systems where a uniform magnetic field is present.

Low-dimensional quantum spin systems in pulsed magnetic fields

Low-dimensional spin systems in high magnetic fields reveal new and unexpected physical phenomena. Typical examples are the distinct plateaus in the magnetization found in quasi-1d and 2d compounds. Even for the well known case of the quasi-1d homogeneous Heisenberg spin chain or its dimerized variant, unexpected elastic anomalies can be detected in high magnetic fields. Since the exchange constants of these low-dimensional spin systems are of the order of the dominant energy scale, pulse-field experiments are particularly well suited for investigations of the magnetic properties. In this contribution we present and discuss our results for selected low-dimensional compounds such as the homogeneous antiferromagnetic Heisenberg spin chain Cu(II)-bispyrazoldihydroxybenzene, which is a new quasi-1d Cu(II)-coordination polymer, the dimerized spin chain (VO) 2P 2O 7, and the plateau systems SrCu 2(BO 3) 2 and NH 4CuCl 3.

Trial wave functions with long-range Coulomb correlations for two-dimensionalN-electron systems in high magnetic fields

A new class of analytic wave functions is derived for two dimensional N-electron $(2&lt;~N&lt;\ensuremath{\infty})$ systems in high magnetic fields. These functions are constructed through breaking (at the Hartree-Fock level) and subsequent restoration (via post-Hartree-Fock methods) of the circular symmetry. They are suitable for describing long-range Coulomb correlations, while the Laughlin and composite-fermion functions describe Jastrow correlations associated with a short-range repulsion. Underlying our approach is a collectively-rotating-electron-molecule picture, yielding for all N an oscillatory radial electron density that extends throughout the system.

Pulsed field ultrasonic and ESR experiments in low-dimensional spin systems

We present the ultrasonic and ESR results for several low-dimensional spin systems in high magnetic fields up to 50 T. With these experiments, we obtain information on the spin state in high fields, their magnetic excitations and on the interaction of these magnetic excitations with phonons. The deduced spin–phonon coupling constant gives information on the structural properties and their connection to low-dimensional magnetism of the systems.

Universal conductance distribution in three-dimensional systems in high magnetic fields

The nature of the critical point of the Anderson transition in high magnetic fields is discussed with an emphasis on scale invariance and universality of the critical exponent. Special attention is paid to the distribution function of the conductance which becomes size and model independent at the critical point. The fractal properties of the wave function which are related to scale invariance are also discussed.

Experimental issues with mass and wave vector of composite fermions

This is a brief summary of experimental results on mass and wave vector of composite fermions in two-dimensional electron systems in high magnetic fields. In the spirit of the workshop, it emphasizes the difficulties and inconsistencies inherent in the experimental data and in their interpretation.

Magnetoconductance of two-dimensional electron systems in high magnetic fields

The longitudinal conductivity σ xx of electrons on the surface of liquid helium was determined for magnetic fields up to 10 T, electron densities up to 4.8 × 10 8 cm −2 and temperatures around 1.7 K. All measurements follow the Drude-Lorentz model 1/ σ xx ∼ B 2 up to field values for which μ s B ≈ 3. In the quantum limit ( h ̵ ω c ⪢ kT) a 1/σ xx ∼ √B behavior is observed down to h ̵ ω c = kT for the highest density. From these results we estimated a high-field mobility. For densities below 10 8 cm −2 existing theories fit our data in almost the full field range. For higher densities the existing theories describe the magnetoconductivity only in the low-field range using the zero-field mobility as fit-parameter and lead to zero-field mobilities which are in agreement with earlier measurements.

Multifractality and scaling in disordered mesoscopic systems

We suggest a new method for investigating scaling properties of mesoscopic observables and their distributions in disordered systems showing metal-insulator transition. In such systems quantum interference effects lead to multifractal structure of eigenstates on scales much smaller than the correlation length of the transition which can be described by a set of exponents, thef(α) spectrum. The analysis off(α) spectra can be extended to any scaling variable. Multifractality is an indication for broad distributions of these variables. If the transition is governed by one correlation length only then thef(α) spectra of normalized scaling variables must be universal. The critical exponentv of the correlation length is determined by the value α(0) wheref(α) takes its maximum and the scaling exponent of normalizationx∶v −1=α(0)+x. As an illustrative example we calculate numerically thef(α) spectra of eigenstates in the critical regime of 2d disordered electron systems in high magnetic fields. We find similarf(α) spectra indicating universal log-normal distributions of scaling variables.

ChemInform Abstract: Magnetic Excitations in Random Systems in High Magnetic Fields

ChemInformVolume 20, Issue 49 Reviews ChemInform Abstract: Magnetic Excitations in Random Systems in High Magnetic Fields J. TUCHENDLER, J. TUCHENDLER Lab. Dispos. Infrarouge, 75252 Paris, Fr.Search for more papers by this authorK. KATSUMATA, K. KATSUMATA Lab. Dispos. Infrarouge, 75252 Paris, Fr.Search for more papers by this author J. TUCHENDLER, J. TUCHENDLER Lab. Dispos. Infrarouge, 75252 Paris, Fr.Search for more papers by this authorK. KATSUMATA, K. KATSUMATA Lab. Dispos. Infrarouge, 75252 Paris, Fr.Search for more papers by this author First published: December 5, 1989 https://doi.org/10.1002/chin.198949338Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue49December 5, 1989 RelatedInformation